1. Field of the Invention
The present invention relates to a process for applying a thermally attached lubricating coating to the interior wall of a cylindrical medicinal container, which has a tapered outlet on one end and a slidable elastomeric stopper acting as a plunger or piston at the other end of the container. The invention also relates to an apparatus for performing this process.
2. Related Art
Containers for medicinal purposes, especially pharmaceutical containers or containers for diagnostic purposes, have slidable elastomeric closure devices, such as pistons or piston stoppers. The slidable elastomeric closure device for these containers is inserted in an interior chamber in a hollow body of the container and slides lubricated on an interior wall of the hollow body. Syringe cylinders of fillable syringes, injector bodies of cylindrical ampoules and containers are typical examples. However other examples include the piston burettes used in analytical chemistry. In order to solve this problem correctly a silicone-lubricating coating is often applied to the interior wall of the hollow body.
The fillable syringes are of special significance here. Fillable syringes made from glass have been disclosed and are known from many years from numerous publications. These fillable syringes comprise glass, which does not have an integrated needle. Glass syringes with attached needles are notoriously well known.
This sort of fillable syringe made from glass requires a lubricant between the movable elastomeric piston or plunger and the glass syringe cylinder. Silicone oil is preferred for this purpose. This silicone oil is usually applied by washing the interior of the injector cylinder. Great differences exist between the processing syringe bodies with and without needles. Since the needle is usually attached with glue, such as epoxy resin, or other adhesives, that have limited heat resistance different process conditions are required.
A maximum processing temperature of 130xc2x0 C. is allowed at the site of the glue or adhesives in finished syringes with hollow needles attached with an adhesive or glue. An adherent lubricant coating is only guaranteed however, when the lubricant, preferably silicone, is applied at temperatures of about 300xc2x0 C.
Thus it is known to provide a glass syringe cylinder with a silicone coating at about 300xc2x0 C. and then subsequently to connect a needle-supporting piece with the syringe body that is made from glass. However this method requires additional assembly effort and thus additional costs, which make it considerably disadvantageous, because it is a mass-produced product.
If a silicone lubricant coating is applied to a syringe with a needle already attached to it, there is a risk that the often very narrow needle duct is filled with silicone lubricant, which can lead easily to unintended injection of silicone oil in application.
This problem also exists in pre-filled plastic syringes. DE 197 53 766 A1 describes a method for providing containers for medicinal purposes with an interior silicon coating. These containers comprise an elongated plastic hollow body, especially a syringe cylinder. The silicone coating is provided by special reactive silicone oil, which hardens under the influence of light. This method avoids the otherwise conventional step of pre-conditioning the interior surface, e.g. by plasma treatment.
It is an object of the present invention to provide a process of the above-described type for providing a thermally attached lubricating coating on an interior wall of a cylindrical medicinal container, which has a tapered outlet at one end and an elastomeric stopper at the other end, which is slidable like a piston in the container, which process is conducted, so that a thermal bonding of the lubricant to the interior wall is possible at very high temperatures without damage to temperature sensitive parts at the outlet end of the container.
It is another object of the present invention to provide an apparatus for performing the improved process according to the invention.
According to the invention this process comprises the steps of:
a) applying a thermally attachable lubricant to the interior wall of the container in a known manner;
b) homogenizing the applied lubricant on the interior wall to form a lubricating coating; and
c) thermally attaching the lubricating coating by irradiating the lubricating coating with infrared radiation selectively in a cylindrical region of the container at elevated temperatures above a maximum operating temperature of the container.
The apparatus for performing this process according to the invention comprises
means for applying the thermally attachable lubricant from a supply reservoir to the interior wall of the container;
means for homogenizing the lubricant applied by the means for applying to form the lubricating coating; and
a rod-shaped infrared radiation source insertable into an interior space in the container, said radiation source having a radiation screen or barrier for keeping the radiation away from the container outlet.
By means of selective heating of the container wall with the infrared radiation the lubricating coating or layer applied to it can be reliably attached in a simple manner and at a high temperatures, while the outlet of the container remains free of lubricant and the attachment of the syringe or injector needle is not damaged. At the same time the germ count and the endotoxins are reduced because of the high temperatures. Furthermore the method according to the invention does not require pre-conditioning of the surface to which the lubricant is applied, e.g. by plasma treatment.
The method according to the invention and the apparatus for performing that method are thus advantageous for applying a thermally attached lubricating coating, especially a silicone coating, both to glass or plastic syringe bodies with integral needles and without integral needles.
Preferably the silicone oil used as the lubricant in the method according to the invention should be reactive silicone oil, non-reactive silicone oil or a mixture of both types of silicone oil. Other thermally fixable or attachable lubricants can be used.
According to a preferred embodiment of the invention the lubricant is applied by spraying, which leads to a relatively uniformly wetting silicone coating in a very simple manner. However other known methods for applying lubricants, especially silicone oils, are also conceivable.
The temperature range for the thermal attachment, among other things, depends on whether or not a glass or a plastic container is to be coated. The temperature range is preferably at about 300xc2x0 C. in the case of glass containers.
For plastic containers the thermal attachment should be performed in a temperature range, which is about 50xc2x0 C. above the maximum operating temperature of the plastic container.
For selective irradiation of the interior wall of the container the rod-shaped infrared radiation source has a preferably top-side covering member in the form of a cylindrical cap acting as a radiation screen or shield. Alternatively the screen can be a mushroom-shaped body, which is attached with its stem to the top end of the radiation source and which keeps the infrared radiation away from the outlet of the container. Other forms of the screen or shield are conceivable.